The present invention relates to an apparatus for controlling the temperature of a liquid to a predetermined level and, more particularly, to such an apparatus of the type which efficiently and safely performs a temperature buildup control from a non-controlled temperature to a desired reference temperature, as distinguished from a usual or normal control which will follow the buildup control.
A liquid temperature control apparatus is known which uses a heater or like heating element to heat a liquid up to a given desired level. Such an apparatus usually comprises a sensor for sensing a liquid temperature and producing a voltage indicative of the sensed temperature, a heater for heating the liquid, a reference voltage source for generating a predetermined reference voltage, a differential amplifier for comparing the output voltage of the sensor with the reference voltage to produce their voltage differential, a heater drive for supplying a drive power to the heater in accordance with the voltage differential, and a timer for causing the heater drive to operate for a predetermined period of time. This type of prior art apparatus can prevent the liquid from being overheated or thermally overshot beyond the reference temperature, since the timer permits the heater drive to operate and, therefore, the liquid to be heated only for its operating period of time.
However, a drawback still results from the operating time period of the timer which is so selected as to promote an optimal buildup of the liquid temperature when the liquid temperature is at a usual or normal level. Even when the liquid temperature before controlled by the apparatus is substantially equal to or only slightly lower than a desired target or reference temperature, for example, the liquid is forcibly heated at least during the operating time period of the timer despite that such heating is hardly needed. This invites wasteful consumption of time and energy. Meanwhile, when the liquid temperature before a control is far lower than the reference temperature, that is, when the operating time period of the timer is short for the heater to sufficiently heat the liquid, a long period of time must be consumed until the reference temperature is reached by the liquid.